Cummins 3.9 into 756 Gasser

Bill VA

Well-known Member
Posted this on another forum to.....


Considering my back-up option on the rebuild of my 756 gasser - if the cost is close.

I get the impression that a 5.9 is the most talked about repower, but might be overkill for a 756. What about the 3.9L Cummins diesel into a 756 gasser? I think Leamans has an adapter kit that fits both the 5.9 and 3.9 engines.

My thought is a 3.9L might be lower cost as I gather it is not as coveted as the 5.9 ? Also the 3.9L is shorter and with it might fit-up better lengthwise and possibly keep the sheet metal and frame rails original?

Anyone put a 3.9L Cummins in a gas or diesel 706 or 756? I'd like to retain the same PTO hp or maybe gain a bit, not interested in pulling or blowing the rear. Just want a nice haying/chore tractor.

Still of the mind I'll rebuild the C291, but again, if a diesel swap is close in cost, might move in that direction.

Thanks!
Bill
 
I did some pencil pushing on this and by the time you buy the engine buy what ya need chop the fuel tank and all the stuff you have to do IF your lucky you can do this for around five grand with NO labor , providing you got and engine with some life left in it . One thing people over look is that unless you get and industrial app engine you need to swap the injection pump from and automotive to a constant RPM pump . Also what i have seen is that the 3.9's bring more money . The 3.9 and 5.9 have a taller stand out from center line of crank So this would mean cutting the tank to clear the vale cover . with the 3.9 you have to come up with a way for the fan to move forward so some barn yard engineering will be required . It will not be just a drop in deal. The essayist Cummins swap is in and Oliver as we have done a 3.9 two 5.9 and one 8.3 and they were not just a drop in affair and they all ran at or close to five grand in a tractor worth five grand running . The 3.9 when worked the rad is not big enough and over heats the 2 5.9 's run ok and the 8.3 the way it is set is way more then the tractor it is in needs , but the 5.9 would not have been enough , even with ft wheel assist and the big tires horse power is not the problem . Traction is . we put it on the deep till this year for the first time as at my one budy's place the ground has gotten so compacted from years of no till and years of corn chopping with the heavy wagons and truck that even with brand new deep suck plow shears the plow would not go into the ground So out comes the tool with five DMI parabolic shanks with the 7.5 inch points BUT when you hit a real hard spot that 8.3 never slowed down and before you could get to the clutch pedal when she broke traction she was bouncing all four wheels off the ground and you getting throwen around in the cab while trying your best to find the clutch pedal. This tractor with all four tires loaded and a huge amount of ft slab weights weighs in over 24000 lbs. at some point something is going to break .
 
Bill,
I suspect you would have very little trouble trading your 756 gas for a 756 diesel for less than $2000 and still make it home for tonight's supper. An engine swap will need a lot of labor and a lot more money than simply trading usable tractors.
 
Lets see a picture of this. I pull 7 shank deep till with a CIH STX 535. You must be going about 4 inches deep.
 
Add a one inft. of the 4 and we normally pull it with a 1066 . DMI block man told me that there was noway a 1066 would do it , welp he had to eat his words the 1066 will haul it and at 14 inches , yep the 1066 has enough snort to spin the rims inside the tire, the only problem we have is we do not have the traction for going up hills , so there is some dead heading on the hilly ground but what little flat we have i can run high 1 with the T/A in high at 2600RPM . The oliver is a 2150 ft assist here again traction is a problem and the oliver will haul it in fourth high .
 
Here are a few pictures of a 3.9 in a 806 frame. This tractor was at RPRU in Albert Lea, MN a few years back.
1580.jpg
1581.jpg
 
just put a 3.9 in a ford pickup. and it made a truck out of it.25 mpg and all the power ill ever need. But a used motor was $3400 shipped from ohio. now I could of bought a 5.9 for $1500. your going to spend a lot of time and more money if you decide to go that rought. Bob
 
I must be living in the wrong place. Where is this magical land where you can trade a 756 gas with a clapped out engine for a field ready 756 diesel for $2000?

Any machinery dealer around here with a 756 diesel in ANY condition wants $10,000 for it, because it's "old" and "rare" and "collectible", but they won't even look at your 756 gas because the engines are "bad news." Of course if you give it to them they will gladly put it on their lot with a price tag of $7500+.

Some day I would like to sit down with a machinery salesman about a tractor they have for sale and say, "Look, you know and I know that tractor will never sell at that price. You're going to put it in your September auction and take whatever you get, which will probably be about 1/3 of what you are asking. Tell me, what does paying all this extra money now get me?"
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top